In textile laboratories, especially of spinning mills, spot checks are carried out on random samples by way of quality control to determine certain textile parameters such as fluctuations in weight and other characteristic quantities which can be derived from these measurements. These tests are carried out by means of so called uniformity testers of the kind, for example, which are distributed world wide by Zellweger Uster AG under the registered trademark USTER.
Typically a uniformity tester includes a measuring unit containing a guide device, a measuring instrument, a feed device and a draw-off device for the sample to be tested. The measuring instrument itself is formed by a measuring comb with plate-like projections defining gaps of different widths between them through which the sample may be passed to determine the characteristic magnitudes. Each measuring gap is the air gap of a capacitor, and the aforesaid magnitudes for the sample are measured capacitively.
In the known uniformity testers, the samples pass through the measuring unit while being stretched between other components, e.g. between the guide device and the draw off device. The sample is inserted into the measuring gap whose width is suitable for the particular sample, and this procedure generally causes it to be deflected from its normal position between the guide device and the draw off device.
In attempts to provide further improvement to this known uniformity tester with a view to obtaining very exact and representative measurement results, it has been found that one important factor is to ensure that the material being tested will always take up the same position, as far as possible, in the measuring unit. Every deflection of the material from its normal position results in undesirable deviation.
Also to be considered are the operational aspects of inserting the sample into a particular measuring gap and removing it therefrom. To determine the fluctuations in weight of the sample to be tested, the sample is pulled through one of the gaps of the measuring comb by the feed device, the choice of measuring gap being determined by the fineness or yarn count of the material. An insertion mechanism for the sample to be tested is associated with the measuring unit. This mechanism grips the material and inserts it into the predetermined measuring gap.
Since it is necessary to adjust the measuring unit to zero or check the zero setting at least at the beginning of each measurement, the test sample already inserted in its measuring gap must be briefly removed from the gap. This had hitherto to be carried out manually by the operator.
However, removal of the test sample from the measuring gap by hand for adjusting the apparatus to zero not only constitutes a source of error but also is not operator friendly.